High speed printer

ABSTRACT

A technique and apparatus for increasing the speed of a printer through the elimination of lag times and the full utilization of a continuously rotating disc-like print element is disclosed. The apparatus includes a continuous drive for translating the print carrier along the print line of a printer while superimposing upon this uniform constant velocity drive a second drive force and velocity from a second drive member to cause the carrier to either be accelerated or retarded to properly position a character independent of the amount of time required to bring the next succeeding character into print position.

United States Patent Battie 1 51 Sept. 30, 1975 HIGH SPEED PRINTER 3.789.97l 2/1974 Deycsso 611 all 197/18 3,800,933 4/1974 7 Taylor l97/49 [75] lnvemormace Lexmgton, 3,817,367 6/l974 Tramposch et 21L... 197/18 73 Assigneez International Business Machines 3,872,960 3/l975 Gabor l97/53 Corporation, Armonk, NY. A Primary E.\'aminerPaul E. Shapiro [22] Flled 1974 Attorney, Agent, or FirmLaurence R. Letson [21] Appl. No.: 537,213

[57] ABSTRACT U-S. t A technique and apparatus for increasing the peed f [51] Int. Cl." B41] 7/44; B4l.l 19/00 a primer through thevelimination of lag times and the 1 Fleld of Search l97/ 48-54; full utilization of a continuously rotating disc-like print 178/34 element is disclosed. The apparatus includes a continuous drive for translating the print carrier along the [56] References C'ted print line of a printer while superimposing upon this UNITED STATES PATENTS uniform constant velocity drive a second drive force 3.356.199 12/1967 Robinson 197 54 and velocity from a Second drive member to Cause the 3,371,766 3/1968 Staller 1 1 197/53 carrier to either be accelerated or retarded to properly 3,448,844 6/1969 Gassino et a1. 197/18 X position a character independent of the amount of 356 .23 2/ 1 b rly et al- 97/ time required to bring the next succeeding character 3,675.753 7 1972 Perucca 197/49 X into print position 3 7l9 l39 3/l973 Niccolai..... 197/53 X 3,757,922 9/1973 Sweeney [97/49 19 Claims, 5' Drawing Figures CONTROL US. Patent Sept. 30,1975 Sheet 1 of3 3,908,809

FIG-.1

CONTROL US. Patent Sept. 30,1975 Sheet 2 of3 3,908,809

ECIAL 14MO TENU ACTERS LOWE ECHA RS 4 8\ 9 II 0 7 60F THE TWELVE LEAS 0 LOW SE L M i ER CASE CTERS 14 MOST 0 LOWER CA FTEN USED SE CHARACTERS PECIAL WEE US. Patent Sept. 30,1975 Sheet 3 of3 3,908,809

FIG. 5

LAST CHARACTER POSITION T02\ ADDER ADD 40 SUB H2 [F 412 f LOAD VALUE OF 104 a L w RESET INCREMENT W COUNTER COUNTER EQUALS HZ 108 ROM CHARACTER 120 LOOK UP 0\ MATCH CHARACTER T NO MATCH 35 (STARTS AT INITIALIZE M|NUS 5) EXCLUSIVE OR &

= DEOREMENTER :j ST EPPER 152 L MOTOR CONTROL STEPPER MOTOR DELAY ss COMPARE {28 LOAD -5 W COUNTER L K n2 HIGH SPEED PRINTER BACKGROUND OF THE INVENTION Printers which utilize a constant velocity translation along the print line and do not stop the carrier have in the past used rotating cylinders with the characters positioned upon a helix such that for each complete revolution of the print wheel, the print point remains relatively stationary with respect to the printed page. This concept has also been implemented on rotating discs such that the characters are displaced radially from the center of the disc in a spiral precession such that the print point remains fixed for any one revolution.

This technique of precessing the characters radially on a flat disc requires that the print point be located at either the three oclock or nine oclock position when viewing the disc perpendicular to its plane. Efforts have been made to move the print point to the twelve oclock position at the disc and then displace the character sequentially by a small increment laterally. The primary problem with this technique is that it requires some very drastically displaced characters on the print wheel thus reducing design flexibility and the ability to position the print properly.

The need for a continuously translating carrier is brought about as a result of a need for increased speed of printing. Impact printing on a serial printing basis is limited in speed principally by the time that it takes to move between successive characters, the time to displace the print position, and the time for impact related transient conditions to settle out. The character selection times and thus the printing speed may be reduced or at least minimized by impacting the character against the record page on the fly, or as the disk spins, to eliminate the time required for stopping and starting the type element and for the elimination of the transient condition settle out time. Thus the eliminating of the starting and stopping of the carrier and the printing disc can minimize the amount of time necessary to print a character and thus improve print throughput.

Without some compensating scheme for maintaining a uniform print point distribution, the print point will be distributed irregularly as a direct result of the variations of displacement between successive characters on the print wheel'or print element and therefore the variation in the times between the presentation of one character and the presentation of succeeding character at the print point. Thus it can be seen that two characters which appear very closely together on the print wheel could be overlapped or superimposed on each other while two characters which are displaced by a very great distance will result in a gap or spread between the printed images.

In the past, this problem has been overcome by continuously rotating the disc but incrementing the carrier upon which the disc is mounted for rotation, in set increments much as a typewriter escapes. The carrier is incremented forward a set distance and then the print element is caused to impact onto the page at the time the appropriate character is presented at the print point. It is clear then that with the carrier incrementing and then stopping to be in the correct position, the time for the printing of a particular character is dependent upon its spacing from the last character printed and dependent upon the amount of time required to increment the character one letter space. The time required to print any character therefore becomes the longest of the above two times.

OBJECTS OF THE INVENTION With these handicaps of the prior art recognized, it then becomes an object of this invention to increase the speed of printing using a serial impact printer with the existing printer discs speeds by eliminating the starting and stopping of the disc and the carrier and superimposing upon the movements of the carrier, a second movement to accurately position the print point at any one time, depending upon the distance and time separating the successive characters.

Another object of this invention is to increase the speed of printing using a serial impact printer of the rotating disc type, using existing printer technology, by duplication of the character set to reduce the amount of time between successive characters.

SUMMARY OF THE INVENTION The foregoing objects are accomplished and the handicaps of the prior art are overcome by superimposing on the movement of the disc carrier, a second motion or corrective displacement. This is accomplished by the utilization of a knowledge of the distance between characters on the print wheel and determination of the amount of time necessary to rotate the print wheel from a first position to a second position and the conversion of that time factor into a distance which the print wheel carrier will traverse at constant velocity during that time. It is then possible to determine the variance between that distance and a predetermined and .predesignated increment between character print positions. A stepper motor is then caused to be fed the appropriate number of control pulses causing the stepper motor, through the mechanical connections to the carrier, to superimpose onto the movement of that carrier either an additional movement or a subtractive movement of an appropriate amount to position the carrier at the desired print point when the character to be printed is next presented at the print point.

The superimposed motion or displacement which is added to or subtracted from the constant velocity displacement of the carrier under the control of its main drive, may be accomplished in several ways. One technique is to use a stepper motor driving a compensating drive cord arrangement as illustrated in FIG. 1.

A second technique is to use a rotatable drive nut in connection with a rotating lead screw. By rotating the drive nut, the carrier can be either forced to traverse faster or slower than the nominal constant velocity drive.

DRAWINGS FIG. 1 illustrates the drive arrangement for translating a carrier which would then support the rotating print disc, the print disc motor and printing hammer.

FIGS. 2 and 3 illustrate a second embodiment of a device for accomplishing the superimposition of corrective displacement upon a constant velocity carrier drive.

FIG. 4 illustrates a print wheel character layout.

FIG. 5 shows the stepper motor control of FIG. 1.

DETAILED DESCRIPTION The print carrier schematically illustrated in FIG. 1, can conveniently be one such as illustrated in FIG. 1 of U.S. patent application, Ser. No. 427,962, filed Dec. 26, 1973, entitled High Speed Wheel Printer by B. R. Martin.

Referring to FIG. 1, a carrier can may be conveniently supported on rails or rods and made freely movable by using support bearings or rollers. This makes the carrier easy to translate along the writing line and reduces the amount of force required to effect such escapement translation.

For greatest flexibility, the translation forces are conveyed to carrier through pulleys l2, 13 mounted on the carrier. For convenience, pulleys 12, 13 are mounted on the bottom of carrier 10 and thus does not provide structural conflicts with other printer required apparatus.

The cable 14 extends around pulley 12 and is wrapped around a drive drum 16. Drive drum 16 is driven by a constant speed driver motor 18. Cord l4 unwrapping from drive drum 16 is then directed around a tension bias pulley 20. Pulley 20 is provided with a tension spring or other equivalent device 22 to maintain drive cable 14 in tension. Drive cable 14 then is wrapped around pulley 13 in a one half wrap and is directed toward stepper motor drive drum 24.

The cable 14 is wrapped around stepper motor drive drum 24 several revolutions to insure an adequate driving force when drum 24 rotates. Stepper motor drive drum 24 is connected to a stepper motor 26. Stepper motor 26 is capable of stepping a discreet portion of a revolution upon the receipt of an electrical pulse. Thus it is capable of operating in steps or increments.

After having been wrapped around drum 24 for sev eral revolutions to insure positive drive, cable 14 extends around idler pulley 28 and from there back around pulley 12 to reconnect to the portion of cable 14 extending between pulley 12 and constant speed drive drum l6.

Constant speed drive motor 18 is capable of constant velocity revolution in either of two directions.

Inasmuch as the drive cable 14 is an endless cable, it can be fed onto and off of drive drum 16 around the pulleys and stepper motor drum 24 in a continuous manner and does not require a return to any particular position.

The constant speed drive motor 18 is controlled to effect translation of the carrier 13 from one end of the writing line to the other end of the writing line at a constant velocity and the return of the carrier 13 to the beginning of the next writing line.

When it is desired to print while the carrier is moving and at the same time use a constantly rotating print disc or print wheel, A stepper motor 26 may be inserted into the system as well as an additional pulley 28 and idler pulleys 12, 13. With drive drum l6 rotating at an assumed tangential velocity of approximately 14 inches per second, and the stepper motor drum 24 being retained in a non moving state, the translational velocity of the carrier will be equal to one-half of the tangential velocity of drive drum 16. This yields a carrier translational velocity of approximately 7 inches per second.

If the drive drum 16, is rotating in a counterclockwise direction as viewed in FIG. 1, cable 14 will be played out to pulley 12. At the same time as being pulled in from around pulley 20. This will cause the cable between pulley 20 and pulley 13 to be placed in tension and pulled in thus causing a translation of the carrier to the right.

Clearly a drive drum reverse will provide a translation to the left for carrier return.

Referring to FIG. 4, the schematic layout of the print wheel, it can be seen that starting at the top and progressing clockwise, there is a 1 12 character print wheel with a partially redundant set of characters to reduce the amount of time to translate from one character to another. The amount of time to translate from any one character to a second character can be referred to as the access time for the next character.

Starting at the 12 oclock position on the print wheel and progressing clockwise around the print wheel, the print position may be designated as the 14 most often used lower case characters, six of the 12 least used lower case characters, ten numerals, 13 upper case characters, then 13 special characters of the individuals choice, the same 14 most often used lower case characters, the other six of the 12 least used lower case characters, l0 numerals, the other 13 upper case characters and 13 special characters. All characters are placed at an equal radial distance from the axis of rotation of disc and are not precessed but positioned on a radial line of the disc.

The frequency of use of letters for the English lan- Clearly additional characters could be inserted and special characters may be added or deleted as the requirements of the particular environment dictate.

For the sake of illustration, it is assumed that the constant speed drive is capable of providing a one-tenth inch translation in the same amount of time that is takes to access 45 characters past the print point. Thus it would be seen that if two sequential characters spaced 45 character positions apart on the print disc, the second character will arrive at the print point at precisely the same time as the carrier arrives at the print point, using only the constant speed drive drum. Obviously this condition will rarely be met and therefore adjustment must occur.

Referring to Table II, it is clear that it can be assumed that the accessing time or character time column provides a requirement of no correction for 45 character times between sequentially printed characters. Similar analysis of the relation reveals that for these assumptions, each character time deviation from the assumed nominal 45 character times between sequential characters results in a 0.00222 inches correction. Thus for the sake of illustration, selected character times are listed in Table II, 40 character times through character times at 5 character time increments and from 70 to 150 character times in character time increments.

TABLE 11 10 Pitch l2 Pitch Constant Ve- Constant locity Drive Correction Velocity Drive Correction CT Displacement Required Displacement Required 40 .089 +.0l l .074 +009 .100 .000 .08 3 .000 .l l 1 .01 l .092 .009 .122 .022 .101 .018 .133 .033 .111 .028 .144 .044 .120 .037 .155 .055 .129 .046 .177 .077 .148 .065 .200 .166 .083 100 .222 "1122 .185 .102 .244 .144 .203 .120 .266 .166 .222 .139 .288 .188 .240 .157 .311 .211 .259 .176 .333 .233 .278 .194

The overdrive column yields the amount of distance that is necessary to displace the character from the position that it would assume as a result of the drive ro'tation alone to a uniform ten pitch placement. The plus 0.01 1 for 40 character times indicates that the carrier must be displaced an additional 0.01 1 from the position that the carrier will occupy at the 40th character time in order to properly position the next letter to be printed.

As a further example, if two characters which are to be printed are separated by 80 characters on the print wheel, a displacement backward or a negative displacement of 0.077 is required to offset the excessive displacement accomplished by the drive drum 16 during the time between the presentation of character number 45 and character number 80 at the print point. This overdrive or correction is superimposed upon the driving effect of the drive drum 16 by stepper motor 26. Stepper motors are generally commercially available and have a rotational step of a designated number of degrees of rotation. By the appropriate sizing of the drum diameter of drum 24 and the selecting of a stepper motor having an angular step of known desired size, it is possible to convert those variables into a number representing number of steps which are required to compensate for one character time difference from the nominal 45 character times. Thus in the event, for example, that it was necessary through proper drum diameter selection to step a stepper motor 3 to compensate for each character time away from the nominal condition of 45 character times and two characters to be printed were separated by 80 characters, a correction for 35 of the 80 characters would be required and thus 35 pulses could be fed to the stepper motor thus converting the 35 pulses to 0.077 of an inch lateral translation in the backward direction. Thus the print point of the print wheel would be properly positioned for printing upon the arrival of the next sequential character.

A like analysis is appropriate in all cases, and a 12 pitch analysis is included in Table II. The only possible condition which should be considered other than the above would be that minimum amount of time which must transpire between the printing of the first character and the presenting the second character for printing which will allow the mechanical components of the system to properly function. Arbitrarily and for the sake of example, it may be assumed that for any two letters that are spaced less than 40 character times apart on the print wheel will not provide sufficient time for hammer recovery and in such case it then becomes necessary that the character times between the two letters not be the shortest number but rather the character time between the printing of the first letter and its second presentation at the print point. The dynamics of the print hammer and other mechanical elements in the printing system may require a time longer or shorter than 40 character times depending upon the design of the system. This may be readily determined for any particular system by the operation of the system and appropriate timing experiments and cannot be rigidly determined here.

A similar table may be devised where each character is assigned an escapement value and corrections may be made to provide proportional spacing by varying the print point spacing accordingly.

1n the event that two characters are spaced 40 character times apart, then the drum 24 of stepper motor 26, using the assumptions of the above example, would be pulsed to cause the drum 24 to rotate in a clockwise direction as illustrated in FIG. 1, a total of 15. This would be accomplished by five pulses of a predesignated polarity as required by the installation of the stepping motor to the motor 26. This would occur during the time that drive drum 16 was rotating at a constant velocity in a counterclockwise direction incrementing carrier 10, a total distance of approximately 0.089 of an inch. The 0.089 of an inch attributable to the drive drum 16 rotation plus the 0.01 1 of an inch attributable to the stepper motor drum rotation yieldsa one-tenth inch increment between printing of characters, the desired spacing.

The foregoing discussion has been made with respect to a 10 pitch printer, where it is desirous to place characters at increments of one-tenth inch spacing.

A similar analysis may be performed for any desired pitch, merely changing the mechanicaldimensio'ns and resizing drive drums and stepper motors to accomplish the desired linear drives in response to known constant speed drive motor operation and also the increments of rotation accomplished on a purpulsed basis from the stepper motor.

. The necessary timing and input signals for firing the print hammer require only minor and modifications,"if any, of existing data processing equipment and one illustrative example of controls for the firing of print hammers in coordination with the selection of characters on the disc printer is illustrated in US. patent application Ser. No. 427,962, Dec. 26, 1973, in the name of B. R. Martin, entitled High Speed Wheel Printer.

FIG. 1 includes a stepper motor control 60 for providing the necessary pulses to the stepper motor of the proper'polarity to over drive or superimpose the corrective displacement upon carrier 10. Stepper motor control 60, may be specially designed and fabricated control or it may be implimented by a general purpose computer which has been programmed to provide the necessary control pulses. v

For sake of illustration, FIG. 5 illustrates a control circuit 60 which provides the necessary pulsesias',a function of the distance and hence t meberwgea characters on the print wheel. I j 2 FIG. 5 illustrates the control circuitry generally identified in FIG. 1 as control 60. The control 60 is provided with a register 100 for storing the last character position. This register 100 stores the position on the print element 8 of the last character which was printed. The output of this register is then passed to an adder which adds 40 to the previous character position. The fourty added to this by adder 102 is representative of the 40 character times or the 40 character displacement which is arbitrarily designated as the minimum recovery time for the firing apparatus 7 and hammer 9 of the printer.

This new address is then passed into a subtractor and if the address exiting from adder 102 exceeds 112, the number of characters on the print disc or print element 8, then 112 is subtracted.

The new address either from adder 102 or from subtractor 104 as the case may be, is loaded into counter 106. Counter 106 is incremented in response to a clock pulse and other conditions as will be discussed below. AS the counter contents are incremented, the value of the counter is inputted to the read only memory 108 to look up the character which corresponds to that character address. The character which corresponds to each sequentially indexed address is then provided to the compare circuit 110. Simultaneously with the inputting, from the ROM 108, of each character, sequentially as they appear around the periphery either the print disc 8, a character provided either by a keyboard, memory or other binary input device is inputted on the character in terminal of the compare circuit 110. The result of the comparison will be either a match or no match condition. The most common condition will be a no match condition which then provides a signal to AND block 112 which also receives a clocking input. The output of the AND circuit 112 on a no match condition and a clock pulse provides the equivalent of a clock pulse to counter 106 to cause the counter 106 to increment-by one and thus provide a new address to the character lookup in the read only memory 108. As the addresses emitting from counter 106 increment they also are transmitted back through the feedback loop to a reset which will reset counter 106 when the address reaches 112. At the same time, the same address is outputted to AND block 114.

Upon a no match condition at compare circuit 110, AND block 112 also provides a signal to counter 116. Counter 116 is loaded to start a 5, count through and then increment by ones above zero. Counter 116 may be loaded through a loader which loads a automatically upon receipt of a delayed initialize signal passed through a single shot 120. The initialize signal may be derived from the signal to fire the print hammer 9 or any other desired source. It may be passed through delay 118 and single shot 120 to provide the control pulse to counter 116. At the same time, the output of single shot 120 also provides a load signal to load the contents of subtractor 104 into counter 106 to start the next character processing. The counter 116 is provided with a minus bit line 122 which controls the exclusive or 124 upon the minus bit line carrying a binary 1. As the counter contents of 116 increased and passed zero and go positive the minus bit line will drop. If the minus bit is high the exclusive or 124 acts as an inverter but if the bit line is low, as with positive contents of counter 116, the exclusive or 124 passes the value of counter l16 with no change to AND block 126. The initialize signal is passed through a single shot 128 and ended with the output of exclusive of 124 to cause the loading of either the output of exclusive or 124 or the output of counter 116, both positive numbers, into decrementor 130. Decrementor 130 counts downward in response in response to a feedback signal derived from the stepper motor, thereby allowing the decrementer to decrement by one each time thestepper motor is capable of being pulsed and not too fast. The decrementer provides a pulse out to stepper motor control 132 upon each decrementing of its contents. Minus bit line 122 is anded with the signal from single shot 128 and under that condition, AND block 134 provides a signal to latch 136 which stores the condition that the minus bit is high thus controlling the direction of stepper motor control 132. The output of stepper motor control 132 is directly fed to stepper motor 26 to cause the stepper motor 26 to rotate the required number of increments, in the desired direction.

When the character to be printed compares at block with the character provided by the read only memory character lookup, a match condition occurs which controls AND block 114. The impressing of a match signal on AND 114 allows the passing of the address from counter 106 back to the last character position register 100 for storage. This allows the last character position register 100 to be updated upon the determination of the number of characters separating the last character and the character desired, taking into consideration the necessity to have the characters separated by at least 40 character positions.

If counter 106 must count past a value of 112 then it is necessary to reset the counter to one inasmuch as most counters will be capable of counting to 128 or higher and would thus give an erroneous address.

This is accomplished by counter reset 138 which functions only when counter 106 provides an output equal to 112. The output of single shot provides a load signal to cause the loading of the contents of subtractor 104 into counter 106 at a time when the circuitry has determined that there is match.

At the same time, counter 116 has received all the incrementing pulses that it will receive from AND 112 and has passed the contents of counter 116 through AND 126 to the decrementer 130. Counter 116 has now emptied and may be reset to a -5 as a result of the same signal which loads 104. The gating of the count in counter 116 through AND 126 is a result of the printing of the previous character and now prepares decrementor for the correction necessary for the next character. This also prepares the match/no match circuitry to determine the next succeeding character so that its separation will be in counter 116 upon the printing of the character whos representative correction is stored in decrementor 130.

It should be recognized that for the sake of simplicity in explanation, the stepper motor control 132 provides one pulse for each decrementation of decrementer 130. In the event that the precise location of characters is not necessary and some compromise in character position can be accepted, it is possible to further increase the speed of the overall printing device if the stepper motor becomes the limiting factor, by only providing one output pulse from the stepper motor control 132 for a plurality of signals received from decrementer 130.

For sake of illustration, it may be desirable that only one step of the stepper motor be utilized for a range of five character positions on the print element. In such a case, the decrementer 130 could be decremented times to provide for one stepper motor pulse emanating from stepper motor control 132. v I I One may easily recognize that the parameters of this portion of the circuit may be determinedby one wishing to implement the invention.

Based on the foregoing, it can be readily seen that the compound motion superimposed upon the basis motion of the drive drum can position carrier 10 in a position for printing other than that which is directly derived from the drive drum rotation itself.

An alternate arrangement for providing essentially the same result that by eliminating the drive cables and pulley arrangement, can be accomplished by the utilization of a lead screw, a constant speed motor can drive a lead screw which is journaled in side frame members of the printer. Referring to FIG. 2 or 3 lead screw 40 may be rotated in one direction and by hold ing nut 42 stationary with'respect to the rotation of the lead screw, the nut 42 will translate laterally co-axially along lead screw 40. Inasmuch as nut 42 is rotatably mounted on carrier side frame 44, frame 44 will translate with drive nut 42. Drive nut 42' is attached by a connecting collar 48 to gear 46. Connecting collar 48 to which drive nut 42 and gear 46 are attached is journaled in carrier side frame 44 for rotation and for transmitting the forces from nut 42 to the frame 44 to accomplish translation of the carrier.

Also journaled for rotation on carrier side frame 44 is stepper motor drive gear 50. Stepper motor drive gear 50 is driven by stepper motor 52 upon command.

The driving of stepper motor drive gear 50 causes gear 46 to rotate in the opposite direction to gear 50 and simultaneously rotate sleeve 48 in nut 42. This generates a translational motion relative to the lead screw 40. Thus it can be seen that by the simultaneous rotation of lead screw 40 and the rotation of nut 42, a compound composite motion may be derived analogous to the compound composite motion of carrier 10 as described above with respect to FIG. 1.,

The exercise of calculating the number of stepper motor 26 increments of rotation and the drum diameter 24 is analogous to the calculation of stepper motor 52 increments of rotation and the rotation of the nut 42 as illustrated in FIGS. 2 and 3. It is a fairly straight forward simple calculation to determine the amount of lateral translation of frame 44 for each angular step of stepper motor 52. This is determined by the determination and manipulation of the three variables of pitch diameter of gear 50, pitch diameter of gear 46 and the pitch of lead screw 40. By the use of these three values, and the appropriate conversion from the stepper motor through the chain of drive to the lead screw nut 42, it is possible to determine for any given system the increment of translation of side frame 44 per step of stepping motor 52. The increment of side frame translation may be arbitrary selected and the gear train 46, 50 be designed to affect the desired translation for each stepping motor pulse.

The cable 14 is wrapped around stepper motor drive drum 24 several revolutions to insure an adequate driving force when drum 24 rotates. Stepper motor drive drum 24 is connected to a stepper motor 26. Stepper motor 26 is capable of stepping a discreet portion of a revolution upon the receipt of an electrical pulse. Thus it is capable of operating in steps or increments.

The corrective displacement overdrive schemes disclosed herein may be adapted to a start/stop operation and when such adaptation takes place it is possible to reduce the amount of carriage translation time. In a start/stop system, the time that is required to a print character is the longestof (a) the times required to access the next sequential character on the print disc or (b) the time it takes to translate the carrier from print position to a second position and stop the carrier. With two drive motors resulting in a compound or additive displacement, it is possible to shorten the amount of time necessary for translating the carriage from one print position to asecond print position. By doing so, the time necessary to print any particular character then becomes the amount of time necessary to access the second sequential character on the print disc. This will have no effect on some characters printing times but on some character printing times where the controlling time had been the length of time it took to index the carrier from the first to the second print position, the difference'between the character accessing time and the carriage translation time is saved by the implementation of this scheme.

It is further possibl'e to make slightly coarse adjustments in the start stop mode where the character disc is stopped and the hammer fired dependent upon carrier position. As the carrier passes the desired point the hammer is fired. This may be controlled by a simple emitter arrangement to moniter carrier positions.

It should be understood that all stepper motor corrections are completed in any of the above arrangements prior to the carrier arriving at the print point.

Another modification of this technique is that it could be used in a keyboard controlled typewriting mechanism for operator interactive input and then subsequently used for printout of the previously inputted information. I I i This would be accomplished by the disabling of the constant speed drive motor on the disabling of the lead screw and use only the stepper motor to effect the translation of the carrier in letter-feed increments. After the information'hadbeen keyed into the typewriter and if a subsequent playback copy was to be made much the same as is presently accomplished using magnetic media power typewriting equipment such as the IBM Magnetic Tape/Selectric typewriter or the IBM Magnetic Card/Selectric typewriter, the machine can then be conditioned to provide on the fly printing in response to the electrical control signals in an automatic playback mode of operation and utilize the compound or composite drive scheme disclosed above during this mode of operation. The necessity for high speed during the input phase of the operation of this device is not present and is inconsistent with a constant velocity carriage translation and therefore for keyboard operation it would be necessary to disable the constant velocity carriage translation drive to provide a letter by letter translation as the information is keyed from a keyboard.

While the foregoing invention has been particularly shown and described with reference to a preferred embodiment thereof, it should be understood by those skilled in the art that the foregoing and other changes in form and detail may be made therein without departing from the spirit and scope of the invention.

I claim:

l. A character-by-character printer having a type element positionable to present different characters to a print position wherein the time required to present successive characters varies in dependence upon particu lar succession of characters desired, and means supporting said type element and paper holding means for relative lateral displacement of said print position along a writing line, wherein the improvement comprises:

first means providing a source of continuous motion operatively connected to move said print position in the letter feed direction;

second means operative to superimpose variable incremental motion onto said continuous motion, and

control means for operating said incremental motion means as a function of the selection time between a character just printed and the subsequent character to be printed.

2. The printer of claim 1 wherein said first and said second means operate in timed relation to each other to position said print position at the desired point at the time and desired characters are presented to said print position.

3. The printer of claim 1 wherein said selection time is reduced by said type element comprising at least a partially duplicated set of characters.

4. The printer of claim 1 wherein said type element is continuously moving.

5. The printer of claim 1 wherein said first means comprises a constant velocity drive motor operatively connected to move said print point at a constant velocity in the letter feed direction.

6. The printer of claim 5 wherein said type element is carried by a carrier moveable along said print line.

7. The printer of claim 6 wherein said operative connection is a cable means.

8. The printer of claim 6 wherein said operative connection is a lead screw and nut drive means.

9. The printer of claim 8 wherein said nut of said drive means is rotationally supported on said carrier and said second means comprising a stepper motor driveably connected to said nut for rotating said nut.

10. The printer of claim 5 wherein said second means comprises a controllable stepper motor connected to said operative connection to superimpose said incremental motion.

11. Thprimer of claim l0 wherein said operative connection is a cable means.

12. The printer of claim 11 wherein said stepper motor connection comprises a drive drum and cable wrapped thereon, said cable comprising said operative connections. a

13. A character-by-character printer having a type element positionable to present different characters to a print position wherein the time required to present successive characters varies in dependence upon particular succession of characters desired, and means supporting said type element and paper holding means for relative lateral displacement of said print position along a writing line, and means for impacting said type element onto said paper handling means, wherein the improvement comprises:

first means providing a source of continuous motion operatively connected to move said print position in the letter feed direction;

second means operative to superimposed variable incremental motion onto said continuous motion,

and

control means for operating said incremental motion means to cause said support means to arrive at said print position when a preselected character is at said print position.

14. The printer of claim 13 wherein said selection time is reduced by said type element comprising at least a partially duplicated set of characters.

15 The printer of claim 13 wherein said first means comprises a constant velocity drive motor operatively connected to move said print point at a constant velocity in the letter feed direction.

16. The printer of claim 15 wherein said type element is carried by a carrier moveable along said print line.

17. The printer of claim 16 wherein said operative connection is a lead screw and nut drive means.

18. The printer of claim 17 wherein said nut of said drive means is rotationally supported on said carrier and said second means comprising a stepper motor driveably connected to said nut for rotating said nut.

19. The printer of claim 15 wherein said second means comprises a controllable stepper motor connected to said operative connection to superimpose said incremental motion. 

1. A character-by-character printer having a type element positionable to present different characters to a print position wherein the time required to present successive characters varies in dependence upon particular succession of characters desired, and means supporting said type element and paper holding means for relative lateral displacement of said print position along a writing line, wherein the improvement comprises: first means providing a source of continuous motion operatively connected to move said print position in the letter feed direction; second means operative to superimpose variable incremental motion onto said continuous motion, and control means for operating said incremental motion means as a function of the selection time between a character just printed and the subsequent character to be printed.
 2. The printer of claim 1 wherein said first and said second means operate in timed relation to each other to position said print position at the desired point at the time and desired characters are presented to said print position.
 3. The printer of claim 1 wherein said selection time is reduced by said type element comprising at least a partially duplicated set of characters.
 4. The printer of claim 1 wherein said type element is continuously moving.
 5. The printer of claim 1 wherein said first means comprises a constant velocity drive motor operatively connected to move said print point at a constant velocity in the letter feed direction.
 6. The printer of claim 5 wherein said type element is carried by a carrier moveable along said print line.
 7. The printer of claim 6 wherein said operative connection is a cable means.
 8. The printer of claim 6 wherein said operative connection is a lead screw and nut drive means.
 9. The printer of claim 8 wherein said nut of said drive means is rotationally supported on said carrier and said second means comprising a stepper motor driveably connected to said nut for rotating said nut.
 10. The printer of claim 5 wherein said second means comprises a controllable stepper motor connected to said operative connection to superimpose said incremental motion.
 11. The printer of claim 10 wherein said operative connection is a cable means.
 12. The printer of claim 11 wherein said stepper motor connection comprises a drive drum and cable wrapped thereon, said cable comprising said operative connections.
 13. A character-by-character printer having a type element positionable to present different characters to a print position wherein the time required to present successive characters varies in dependence upon particular succession of characters desired, and means supporting said type element and paper holding means for relative lateral displacement of said print position along a writing line, and means for impacting said type element onto said paper handling means, wherein the improvement comprises: first means providing a source of continuous motion operatively connected to move said print position in the letter feed direction; second means operative to superimposed variable incremental motion onto said continuous motion, and control means for operating said incremental motion means to cause said support means to arrive at said print position when a preselected character is at said print position.
 14. The printer of claim 13 wherein said selection time is reduced by said type element comprising at least a partially duplicated set of characters.
 15. The printer of claim 13 wherein said first means comprises a constant velocity drive motor operatively connected to move said print point at a constant velocity in the letter feed direction.
 16. The printer of claim 15 wherein said type element is carried by a carrier moveable along said print line.
 17. The printer of claim 16 wherein said operative connection is a lead screw and nut drive means.
 18. The printer of claim 17 wherein said nut of said drive means is rotationally supported on said carrier and said second means comprising a stepper motor driveably connected to said nut for rotating said nut.
 19. The printer of claim 15 wherein said second means comprises a controllable stepper motor connected to said operative connection to superimpose said incremental motion. 